The present invention relates to a driving circuit for an electrooptical display containing an electrochromic material held in two electrode carrying support plates to manifest reversible variations in the light absorption properties upon current supplied.
An electrochromic material is one in which the color is changed by the application of an electric field or current. See, for example, L. A. Goodman, "Passive Liquid Displays," RCA Report 613258.
The present inventors have discovered that the degree of the coloration of the ECD (electrochromic display) is dependent on the total amount of changes passed through a unit area. That is, the degree of coloration of the ECD increases as the total amount of charge per unit area is increased. Moreover, the present inventors have discovered that the degree of the coloration does not vary even when the temperature varies as long as the total amount of charge passed through a unit area is maintained at a predetermined value.
Generally, in the electro-chemical phenomenon, the electric current flowing through the system is dependent on the temperature when constant potential is supplied. That is, the electric current flowing through the system becomes small as the temperature becomes low. The ECD has a similar characteristic, that is, the response becomes slow as the temperature becomes low. The present invention is based on the above analysis, and is characterized in that a constant current drive is applied to the ECD, thereby eliminating the influence caused by the temperature variations.
Accordingly, an object of the present invention is to provide an improvement in a driving circuit for electrochromic displays which can enhance legibility of a visual display provided by the electrochromic displays.
Another object of the present invention is to provide a constant current supply drive circuit for the electrochromic displays.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, constant current supply sources are provided for the respective segment electrodes included within the electrochromic display. A common electrode confronting the segment electrodes is maintained at the ground potential.